The Discovery of Type II Superconductors Part 2 pot

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Coordination chemistry and superconductivity. J. Phys. Chem. Solids, 52, 5, pp. 659-663 2 The Discovery of Type II Superconductors (Shubnikov Phase) A.G. Shepelev National Science Center «Kharkov Institute of Physics and Technology» Ukraine “It is a fascinating testament to Shubnikov’s great originality and to the terrible times that deprived him of his life and we all of the fruits of the science for so long. Even now, many do not really understand the breakthrough made in Kharkov.” From the letter of 31 December, 2008, written by Shubnikov Professor D. Larbalistier, Director of Applied Superconductivity Center, USA, on reprinting in English the article (Shubnikov et al., 1937) in 2008. 1. Introduction At present, Type II superconductors enjoy wide applications in science and technology. It is worth noting that all the superconductors, from Nb 3 Sn to cuprates, fullerenes, MgB 2 , iron- based systems that have been discovered for the last 50 years, are Type II superconductors. It is of interest to trace back the intricate research carried out for 8 years from 1929 (De Haas & Voogd, 1929) to 1936 by experimenters in four countries out of the five, who had liquid helium at their laboratories at the time when L.V.Shubnikov, V.I.Khotkevich, G.D.Shepelev, Yu.N.Ryabinin (Schubnikow et al., 1936; Shubnikov et al., 1937; Shepelev, 1938) discovered experimentally in Kharkov the phenomenon of Type II superconductivity in single-crystal, single-phase superconducting alloys. A theoretical explanation of the phenomenon, based on experimental results (Shubnikov et al., 1937) and the Ginzburg-Landau theory (Ginzburg & Landau, 1950; Ginzburg, 1955), was given by A.A.Abrikosov only in 1957 (Abrikosov, 1957). The proposed publication lays out the recognition of the discovery of Type II superconductors by leading specialists in this area and indicates a role which this phenomenon plays in the science and technology. Unfortunately, neither L.D.Landau nor anyone of the pioneer-experimenters lived to witness the awarding the corresponding Nobel Prize 2003 when it was given to V.L.Ginzburg and A.A.Abrikosov. All the superconductors are known to be of two types depending on the magnitude of the ratio: æ=λ/ξ , where æ – the Ginzburg-Landau parameter, λ - the penetration depth of magnetic field, ξ – the coherence length between electrons in Cooper pair (Fig.1). For the typical pure superconductors λ~500 Å, ξ~3000 Å, i.e. æ<<1. A critical value used to determine the superconductor type is the following: æ с = 1/ 2 (Ginzburg & Landau, 1950; Ginzburg, 1955). Superconductor 18 Fig. 1. Schematic diagram of interface between normal and superconducting phases: a) Type I superconductor; b) Type II superconductor. n s – density of superconducting electrons (After Ginzburg & Andryushin, 2006). Magnetic properties of these two superconductor types are essentially different (Fig.2). This phenomenon can be attributed to the fact that in the Type I superconductors (pure superconductors), where the Ginzburg-Landau parameter æ < 1/ 2 (Ginzburg & Landau, 1950; Ginzburg, 1955), the n-s interphase surface energy σ ns > 0. For this reason, under the impact of magnetic field an intermediate state, as shown by L.D.Landau (Landau, 1937; Landau, 1943), is created in those superconductors of arbitrary shape (with the demagnetizing factor n ≠ 0) where the layers of the normal and superconducting phases alternate. (a) (b) Fig. 2. (а) The induction in the long cylinder as a function of the applied field for Type I and Type II superconductors; (b) The reversible magnetization curve of a long cylinder of Type I and Type II superconductor (After De Gennes, 1966) In Type II superconductors (superconducting alloys), where æ > 1/ 2 , the n-s interphase surface energy σ ns < 0 and magnetic field penetrates these superconductors in the form of the Аbrikosov vortex lattice (Аbrikosov, 1957). As indicated by A.A.Abrikosov (Аbrikosov, 1957), the idea about the alloys turning into Type II superconductors at the value of the parameter æ > 1/ 2 was first brought forward by L.D.Landau. The Discovery of Type II Superconductors (Shubnikov Phase) 19 Yet, it took about 30 years since the pioneering experimental research on superconducting alloys under applied magnetic field to understand fully the Type II superconductivity phenomenon. The theory of Type II superconductors has been expounded in detail over the past 45 years in scores of reviews and monographs on superconductivity, the experimental side of the discovery of these superconductors, as far as the author knows, having been discussed only fragmentarily either at the early stages of the research (Burton, 1934; Wilson, 1937; Ruhemann, 1937; Shoenberg, 1938; Jackson, 1940; Burton et al., 1940; Ginzburg, 1946; Mendelssohn, 1946; Shoenberg, 1952) or later on (refer to the authoritative published papers (Mendelssohn, 1964; Mendelssohn, 1966; Goodman, 1966; De Gennes, 1966; Saint-James et al., 1969; Anderson, 1969; Chandrasekhar, 1969; Serin, 1969; Hulm & Matthias, 1980; Hulm et al., 1981; Pippart, 1987; Berlincourt, 1987; Dahl, 1992 1 ; Dew-Hughes, 2001) and also to (Sharma & Sen, 2006; Slezov & Shepelev, 2008; Karnaukhov & Shepelev, 2008, Slezov & Shepelev, 2009)). Therefore, the way the real events took place is, quite regrettably, largely hidden from view to many of the International Scientific Community. We shall remind that H.Kamerlingh Onnes (Physical Laboratory, University of Leiden), an outstanding physicist of those times, who discovered the phenomenon of superconductivity in pure metals in 1911 (Kamerlingh Onnes, 1911), was the first with his co-workers to take an interest beginning from 1914 in the effects of magnetic field on those superconductors (Kamerlingh Onnes, 1914; Tuyn & Kamerlingh Onnes, 1926; Sizoo et al., 1926; De Haas et al., 1926, De Haas & Voogd, 1931a). In particular, it was found that superconductivity in pure metals got suddenly disrupted when impacted by an applied magnetic field with a critical value Н с (in the case of the demagnetizing factor n = 0), which manifested itself in a sudden restoration of electrical resistance of the samples from zero to such value that corresponded to Т>Т с (Fig.3). Fig. 3. Sudden change of electrical resistance of wire sample of single crystal tin at Т<T c , as caused by longitudinal magnetic field (After De Haas & Voogd, 1931a). 1 In the interesting book, Dahl (Dahl, 1992) has erroneously ascribed the discovery of Type II superconductors to some other article from Kharkov. In reality, as is well known (see 4. Recognition), the world’s leading specialists in superconductivity unanimously relate this discovery to the articles by L.V.Shubnikov V.I.Khotkevich, G.D.Shepelev, Yu.N.Ryabinin. (Schubnikow et al., 1936, Shubnikov et al., 1937). Superconductor 20 It should be said that, aside from the feature of electric properties of Type I superconductors upon decreasing temperature below Т с (the steep fall of electrical resistance down to such resistivity which was smaller than 10 -23 Ω·cm), the second fundamental characteristic of pure superconductors (magnetic properties) also had a peculiarity that was out of the ordinary. In 1933 W. Meissner and R. Ochsenfeld (Physikalische Technische Reichsanstalt) found (Meissner & Ochsenfeld, 1933) that a magnetic field which was smaller than Н с did not run through a pure superconductor, the magnetic induction in it being В = 0 (with the exception of a very thin surface layer ~ λ). Under the impact of an applied magnetic field with the value Н с the pure superconductor magnetization M and induction B also changed with a jump (Fig.4). These values are related via the following ratio: М = (В - Н) / 4π. The exclusion of flux from the bulk of pure superconductor is called the Meissner effect. Any discovery is generally preceded by a preparatory period. Then, some day or other, following the actual discovery the recognition is accorded. Some time after that one can look at final results and evaluate the prospects. (a) (b) Fig. 4. a) Magnetization curve of a pure superconducting long cylinder in longitudinal magnetic field; b) B-H curve of a pure superconducting long cylinder in longitudinal magnetic field (After Shoenberg, 1938). 2. Preliminary stage Interestingly enough, even before the Meissner effect was discovered, W.J.De Haas, J.Voogd (Kamerlingh Onnes Laboratory, University of Leiden) had discovered (De Haas & Voogd, 1929) a distinction between the behavior in applied magnetic field of electrical resistance of polycrystals of superconducting alloys and that of pure superconductors. It appeared that in rod specimens of the alloys Bi + 37.5at%Tl, Sn + 58wt%Bi, Sn +28.1wt%Cd (the latter two being close to the eutectic alloy) (De Haas & Voogd, 1929), in the alloy Pb + 66.7at%Tl, the eutectic Pb + Bi and in the alloys Pb-Bi (7wt%; 10wt%; 20wt%), Sn + 40.2wt%Sb (De Haas & Voogd, 1930), in the alloys Pb + 15wt%Hg, Pb + 40wt%Tl, Pb + 35wt%Bi, the eutectic Au-Bi (De Haas & Voogd, 1931b) the disruption of superconductivity occurred across a broad interval of magnetic fields irrespective of the orientation of the field running parallel, i.e. at The Discovery of Type II Superconductors (Shubnikov Phase) 21 n=0 (Fig.5), or perpendicular (Fig.6) to the axis of cylindrical specimens, i.e. at n = ½ 2) . As D.Shoenberg noted (Shoenberg, 1938; Shoenberg, 1952), for superconducting alloys “there is much less difference between the curves for a transverse and a parallel field than there is for a pure superconductor”. (a) (b) Fig. 5. The resistance of superconducting long cylinder for polycrystalline Sn-Bi alloy (After De Haas & Voogd, 1929) and Pb-Tl alloy in longitudinal magnetic field (After De Haas & Voogd, 1930). (a) (b) Fig. 6. Variation of electrical resistance of cylindrical specimens of superconducting alloys Bi-Tl (After De Haas & Voogd, 1929), Pb-Bi (After De Haas & Voogd, 1930) in transverse magnetic field at various temperatures. During studies on the electric properties of the eutectic Pb-Bi, while decreasing applied magnetic field from Н с to zero, (De Haas & Voogd, 1930) found a clear-cut hysteresis about 2 The exact data about the composition of research alloy samples are given: for alloys Sn-Bi, Sn-Cd, Pb- Bi in (De Haas et al., 1929a), Pb-Tl in (De Haas et al., 1930), Sn-Sb in (Van Aubel et al., 1929), Au-Bi in (De Haas et al., 1929b). Superconductor 22 which many authors wrote later so very many scientific papers. Much later, it was shown (Saint-James & DeGennes, 1963) that in the case of the magnetic field that ran parallel to the surface in the interval H c2 < H <H c3 = 1,695H c2 a superconducting layer of the thickness on the order of ξ was formed on the surface of the sample. The problems of the hysteresis and “frozen-in” magnetic flux in such superconducting alloys that, as established later on, were strongly dependent on sample quality (compositional inhomogeneities, impurities, stresses) were discussed in minute detail in monographs by D.Shoenberg (Shoenberg, 1938; Shoenberg, 1952). W.J.De Haas, J.Voogd noted quite reasonably (De Haas & Voogd, 1929), that the eutectic research samples were a mixture of two phases, one of which shunted the entire sample when the electrical resistance was taken. The difference in the disruption of superconductivity of the alloys, for instance Pb +66.7at% Tl and Pb +40wt% Tl, relative to pure superconductors was attributed by the above authors to the possible influence from inhomogeneities in the alloy samples (De Haas & Voogd, 1930; De Haas & Voogd, 1931b). Unfortunately, in the early 20 th century not all of the phase diagrams of the alloys were known precisely. According to data from such a prestigious source as (Massalski, 1987) (Fig.7 and 8) the majority of the alloys studied by W.J.De Haas, J.Voogd (De Haas & Voogd, Fig. 7. Binary phase diagrams of the alloys Tl-Bi, Pb-Tl, Pb-Bi, Sn-Sb (After Massalski, 1987). The Discovery of Type II Superconductors (Shubnikov Phase) 23 Fig. 8. Binary phase diagrams of the alloy Hg-Pb (After Massalski, 1987). 1929; De Haas & Voogd, 1930; De Haas & Voogd, 1931b) (except the alloys Pb+Tl, Pb+Bi (7wt%; 10wt%) and Pb+15wt%Hg) had more than one phase, i.e. they were distinctly inhomogeneous as were the alloys with the eutectics Sn-Bi, Sn-Cd, Pb-Bi, Au-Bi. The discovery in the eutectic Pb-Bi of preservation of superconductivity under applied fields on the order of 2T allowed W.J.De Haas, J.Voogd (De Haas & Voogd, 1930) to bring back to life a dream that had been cherished by H.Kamerlingh Onnes about creating magnetic fields by using superconducting solenoids without wasting much energy. However, neither in Kharkov, nor in Leiden, nor in Oxford this dream was not to come true on account of the low value of the current that acted to disrupt the superconductivity (Rjabinin &Schubnikow, 1935a; Keesom, 1935; Mendelssohn, 1966). Thirty years on, K.Mendelssohn (Mendelssohn, 1964; Mendelssohn, 1966) reasoned that the resolution of this challenge, as it were, called for a change in mentality, a heretofore inconceivable progress in scientific engineering and scope of scientific research, as well as for considerable increases in the funding of the Science. The subsequent experimental research indicated that not only the behavior of the electrical properties, but also that of the magnetic ones, in superconducting alloys were different to the properties of the pure superconductors. In the span of 1934-1936 there was a thrilling “hurdle race” in the studies on magnetic properties of superconducting alloys between scientists of four countries out of the five that had liquid helium at their laboratories at that moment. Considering that the superconductors possessed a large magnetic moment, the methods used in the works below were based on the standard magnetic measurements. Using a fluxmeter or a ballistic galvanometer, the measurements were made of magnetization-vs voltage characteristics in the coil that surrounded the sample: during sample cooling in constant pre- assigned magnetic field or after sample pulling out of the coil at constant temperatures and magnetic fields, or upon turning on and off the constant magnetic field, or during stepping up or down the magnetic field little-by-little across the entire range from zero to Н с and back. Canadian scientists F.G.A.Tarr and J.O.Wilhelm (McLennan Laboratory, University of Toronto) submitted a paper for publication (Tarr & Wilhelm, 1935) on September 14, 1934 which contained the results of their studies on magnetic properties of superconducting mercury, tin, tantalum, as well as the alloys with the eutectic Pb+Sn (40wt%; 63wt%; 80wt%) and the multiphase alloy Bi+27.1wt% Pb+22.9wt%Sn, observable under the impact of applied magnetic field. Fig.9 presents the phase diagram of the ternary alloy. In particular, a Superconductor 24 Fig. 9. Phase diagram of the alloy Bi-Pb-Sn (After Kattner, 2003). study was made on decreasing the magnetic flux running through plane disklike samples during their cooling at a constant magnetic field which was perpendicular to the disk plane (n=1) from a temperature higher than Т с to the temperature corresponding to Н с . Whereas the magnetic flux was completely expelled from the pure mercury sample, in samples of the commercially produced tin, lead, tantalum (evidently of insufficient purity) the “frozen-in flux” was observable. There was no Meissner effect in the alloys that had more than one phase Pb+Sn (40wt%; 63wt%; 80wt%) and Bi+27.1wt% Pb+22.9wt%Sn at all. T.C.Keeley, K.Mendelssohn, J.R.Moore (Clarendon Laboratory, Oxford University) in their paper (Keeley et al., 1934) submitted for publication on October 26, 1934 and published on November 17 of the same year presented the results of induction measurements in long cylindrical specimens of mercury, tin, lead and alloys Pb+Bi (1wt%; 4wt%; 20wt%), Sn+28wt%Cd, Sn+58wt%Bi (pre-cooled to a temperature below Т с ) upon turning on and then off the longitudinal magnetic field (n = 0). It appeared that the “frozen in” magnetic flux, remaining in the sample («frozen in» induction) was zero for pure mercury, but a “small addition of another substance has the effect of “freezing in” the entire flux which the rod contains at the Hc, when the external field is switched off”. The authors reported that at a temperature below Т с in samples of the said-alloys in longitudinal magnetic field “it was observed in most cases that the change of induction did not seem to take place at a definite field strength but, at a constant temperature, extended over a field interval, amounting to 10-20 per cent of the threshold value field”. Let us say that a greater portion of the alloy compositions studied by these authors had been earlier investigated by W.J.De Haas, J.Voogd (De Haas & Voogd, 1929; De Haas & Voogd, 1930; De Haas & Voogd, 1931b); the single-phase alloys being only Pb+Bi (1wt%; 4wt%). On December 22, 1934 in their report at a session of Royal Academy (Amsterdam) W.J.De Haas and J.M.Casimir-Jonker (De Haas & Casimir-Jonker, 1935a) reported the results of studies on magnetic properties of carefully prepared polycrystals of alloys Bi+37.5at.%Tl (multiphase alloy) and Pb+64.8wt%Tl. The samples were cylinders 35 mm long, 5 mm in diameter, with a narrow 1 mm dia. duct running along the axis; the applied magnetic field was incident perpendicular to the axis of the cylinders (n = ½). The measurement of the magnetic field inside the samples was made over measurement of the electrical resistance of a miniature bismuth wire placed in the middle of the duct. Apparently, for both alloys at temperatures below Т с the magnetic field began to penetrate the superconducting alloys only after attaining a certain value of the applied field (Fig.10). The Discovery of Type II Superconductors (Shubnikov Phase) 25 In this way, it turned out that there were three characteristic fields in the superconducting alloy: a weak field of the incipient penetration of the magnetic flux into the alloy, a field of the onset of a gradual restoration of electrical resistance and a field of the complete transition of the alloy into the normal state (Fig.11). Articles covering those studies were submitted by W.J.De Haas and J.M.Casimir-Jonker on December 7, 1934 to the prestigious “Nature” (which ran it on January 5, 1935 (De Haas & Casimir-Jonker, 1935b)) and to the sole low-temperature physics dedicated authority of those times “Communications from the Physical Laboratory of the University of Leiden» (De Haas & Casimir-Jonker, 1935c) (refer also to the paper (Casimir- Jonker & De Haas, 1935) submitted for publication on July 29, 1935). (a) (b) Fig. 10. Penetration of magnetic field into the superconducting alloys Bi+37,5аt.%Tl (left) and Pb+64,8wt%Tl (right). For alloy Pb+64,8wt%Tl curve at 4,21 К obtained for normal state (T>T c ) (After De Haas & Casimir-Jonker, 1935c). Fig. 11. Temperature dependence of the incipient penetration of magnetic field into the superconducting alloy Pb+64.8wt%Tl. The hatched region denotes the region of gradual flux penetration in magnetic field according to the electrical resistance measurement data (After De Haas & Casimir-Jonker, 1935a). [...]... hysteresis rather small 5 The difference in free energy of magnetized and normal superconductors was given by the area of the curve: ΔF = ∫МdH, The Discovery of Type II Superconductors (Shubnikov Phase) 31 where М – the magnetization, while the entropy difference was produced by the derivative: ΔS = – (∂F/∂T)В Fig 17 The induction curve of long cylinders of single-crystals of alloys Pb +2, 5wt%Tl; Pb+5wt%Tl... employed for research into Type II superconductors, since in a broad region of the impurity concentrations there is a region of the solid solution (Fig.7,15) which The Discovery of Type II Superconductors (Shubnikov Phase) 29 was stable down to the cryogenic temperatures, thus opening up new vistas for making studies on the concentration effects Fig 15 Binary phase diagrams of the alloy Pb-In (After Massalski,... defended the first doctoral dissertation at Shubnikov’s Cryo Lab (Shepelev, 1938) was placed at the head of this Lab (Fig 22 ) Then the Second World War broke out and interests of the scientists shifted en masse in other directions After Germany’s aggression against the USSR Shepelev volunteered to the front and was killed in action during the defense of Sevastopol at the age of 36 Fig 22 G.D.Shepelev at the. .. and the greater became Н 2, which corresponded to Shubnikov and colleagues’ experimental results (Schubnikow et al., 1936; The Discovery of Type II Superconductors (Shubnikov Phase) 37 Shubnikov et al., 1937) Also, where in Type I superconductors the superconductivity disruption occurred according to the mechanism of phase transition of the first kind, in Type II superconductors, with Нс1 and Н 2 present,... al., 1937) and the Ginzburg-Landau theory (Ginzburg & Landau, 1950; Ginzburg, 1955), constructed the Type II Superconductor Theory which now could describe, even quantitatively, these experimental results It turned out that the thermodynamic critical field Нc was roughly equal to the geometric average of the fields Нс1 and Н 2: Hc Hc ≈ 2 ≈ 2 ⋅æ Hc 1 Hc Thus, the greater was the value æ, the smaller became... sudden disruption of the superconductivity upon further magnetic field increasing (Fig.16) 2 Upon increasing the impurity concentration beyond that boundary (within the presentday viewpoint: with the growth of the Ginzburg-Landau parameter æ) the magnetic properties of the alloys got to differ drastically from those of the pure superconductors: The Meissner Effect existed only as far as the magnetic field... Evetts, 19 72; Ullmair, 1975; Blatter, 1994; Brandt, 1995; Brandt, 20 09) It took several decades for metallurgists to create the relevant microstructure of the superconductors by way of a complex metallurgical treatment (DewHughes, 20 01; Larbalestier et al., 20 01; Slezov et al., 20 05; Chen et al., 20 09) Type II superconductors are used widely in many areas of science and technology around the globe The most... behavior of alloys is caused by their inhomogeneity which may be due to the decomposition of the solid solution and the formation of a new very disperse phase” (Rjabinin & Schubnikow, 1935a) The Discovery of Type II Superconductors (Shubnikov Phase) 27 On April 3, 1935 K Mendelssohn and J.R.Moore (Mendelssohn & Moore, 1935) submitted a new article (published on May 18, 1935) in which they supported the. .. conflict of creativity and a great human tragedy affecting the lives of two prominent scientists, L.D.Landau and The Discovery of Type II Superconductors (Shubnikov Phase) 33 L.V.Shubnikov, and the directions the Big Physics might otherwise have taken V.L.Ginzburg, a Nobel Laureate, addressing an International Conference of Fundamental Problems of High-Temperature Superconductivity (20 04) had the following... studies of superconducting alloys and a factual discovery of Type II superconductors I am sure that Shubnikov would have achieved even greater success in science, and one cannot but feel bitterness about his untimely (at the age of only 36!), and quite guiltless death under the ax of Stalin’s terror” (Ginzburg, 20 05) Fig 19 The induction curve of long cylinders of single-crystals of alloy Pb+2wt%In; . (Аbrikosov, 1957), the idea about the alloys turning into Type II superconductors at the value of the parameter æ > 1/ 2 was first brought forward by L.D.Landau. The Discovery of Type II Superconductors. parallel to the surface in the interval H c2 < H <H c3 = 1,695H c2 a superconducting layer of the thickness on the order of ξ was formed on the surface of the sample. The problems of the hysteresis. research into Type II superconductors, since in a broad region of the impurity concentrations there is a region of the solid solution (Fig.7,15) which The Discovery of Type II Superconductors